Cold Front Blasts Through Wyoming, Causes Damage

Summary | Bighorn Wind Damage Info | Wind Reports | Fire

A strong storm system moved through the region on Sunday and Monday, its impact was felt across much of western and central Wyoming.
As the storm strengthened to our west, dry southwest flow delivered dangerous fire weather conditions to areas east of the Divide where the abundant grasses have been drying over the past couple of weeks.

Red Flag Warnings, indicating very high fire danger, were issued for Sunday afternoon and again for Monday. Unfortunately these warnings were verified when several grass fires broke out across the region, including a large fire near Bar Nunn, which is part of the Casper metro area, and another fire that started near Lander after a powerline was blown down in the strong wind.

In addition to the wind and fire danger, severe thunderstorms broke out along the cold front. Severe weather reports ranged from downed tree limbs, to strong wind damage in the Bighorn Mountains, destroying between 4 and 7 camper trailers, and snapping/damaging many trees. Findings support straight-line wind damage with no tornado present over the Bighorn Mountains.  Click here to see a compiled list of severe storm reports from Monday.

Very cold air settled in behind the front, with periods of snow falling over the western mountains. Freezing temperatures are expected overnight in the western valleys in addition to the higher elevations.

Click to Enlarge At 3pm on Monday afternoon, the cold front was beginning to move through western Wyoming with the low pressure system responsible for the rough weather rapidly intensifing and moving north. This rapid intensification is in part responsible for the strong wind while the cold front is contributed a focus for severe thunderstorms, and the strong southwest flow lead to high fire danger.

Click to Enlarge It was a strong cold front but how cold was it? It was snowing, large flakes, in the western ski areas before sunset... Photo by JHMR

TOP MENU

A significant amount of instability, moisture, lift, and spin was present in the atmosphere across northern Wyoming on Monday. This creates an environment favorable for straight line winds, microbursts, and tornadoes. These elements worked together to form a severe thunderstorm that tracked through the northeastern quarter of the Big Horn Basin and into the Bighorn Mountains on Monday afternoon.

 

Click to Enlarge After we went out and surveyed the damage, we noticed that the trees were lying in the same direction and there was wind-driven hail damage on the campers that was all on the same side. In addition, the damage occurred quite a distance from where rotation was noted on radar in an area of the storm where tornadoes are not expected.

There were a lot of reports of wind damage, and this area of the Bighorn Mountains is notorious for straight line wind damage. NWS Riverton conducted a damage survey on July 28th. Some of the findings from the damage survey include:

• The damage path was at least 0.4 miles wide and 3.6 miles in length
• The damage was consistent with 90-100mph winds
• All damage was noted just inside the border of Sheridan county, which is covered by the NWS office in Billings, MT
• Damage was representative of straight-line winds with no tornado signatures apparent
• Multiple trees (including large ones) were uprooted, snapped, or topped
• 2 campers were observed to be destroyed with 2 additional campers having significant damage. The other 3 campers initially included in reports were not onsite, but it is unknown if they were never there or just moved.
• Zero injuries/fatalities have been associated with this severe wind event
  
   

Damage Video Damage Map

Trees Uprooted	The Bottom of the Camper	The Rest of the Camper	This Camper Was Also Destroyed

Top of a Tipped Camper	Trees Fell Around This Camper	Large, Healthy Trees Snapped	Tree Damage Extended For 3.6 Miles

TOP MENU

Strong winds developed ahead of the cold front as fast flow aloft was easily mixed down in the hot afternoon air. Widespread 30 to 40 mph winds were accelerated by thunderstorms that developed in the afternoon. Some of these storms produced wind gusts in excess of 70 mph and caused damage across large swaths of western and central Wyoming. Most of the damage reports included tree limbs down, but there was also a report of the strong wind causing a power line to topple over near Lander and start a wildfire. There were also reports of carports damaged in Hayatville, Wyoming.

Click to Enlarge A Strong wind along with the cold frontal passage kicked up a significant amount of dust and dirt as it barreled through the town of Riverton. Photo Credit: Iris Redcliff	Click to Enlarge There were several reports of trees down and limbs broken across central Wyoming. This tree limb was broken outside of a home in Basin, Wyoming. A nearby station in Greybull, Wyoming recorded 60 mph winds. Photo Credit: Julie Birchfield

Click here to see a pop-up list of the highest winds reported during this event.

TOP MENU

A large fetch of hot, dry air was fed in ahead of the approaching storm system, leading to elevated fire danger across much of the state on Sunday and especially on Monday as winds increased.

After a couple of slow fire seasons and a wet spring and early summer, there was plenty of grass and other fine vegetation ready to burn after just a couple of weeks of hot, dry weather. A few dry lightning strikes and some strong Wyoming winds was all it took to get some of these fires started, the cause of some of these fires remains under investigation.

The "good" thing about these big events is that they usually advertise themselves well. Messaging about the high fire danger on Sunday and Monday begain on Thursday of last week with our first ever event-driven Multimedia Fire Weather Briefing issued on Friday to highlight the complexities of this system. The first Red Flag Warning for this event was issued on Saturday, with an average of 34 hours of lead time for the Monday event, 16 hours for the Sunday event. 

There were two fairly high-impact fires. One occurred near Bar Nunn (Casper Metro Area) that prompted an evacuation order and closed several roads and off ramps along Interstate 25. The fire is rumored to be caused by lightning and ended up scortching a couple of fences but all lives and homes in the area were spared. The other wildfire was started when power lines were blown down by the wind in the Lander foothills. Power was out for over 5,000 residents of Lander and Hudson for several hours and it took firefighters even longer to extinguish this wind-driven blaze.

Click to Enlarge The Bitter Creek Fire was ignited on Sunday just south of Rock Springs. This fire was burning actively through about 4am on Monday morning. The cause and total acreage are still under investication. Photo Credit: Brandi Smith	Click to Enlarge   Messaging about the event began at the end of last week.

Click to Enlarge   A fire near Casper prompted voluntary evacuations on Monday. The fire burned approximately 600 acres. Photo Credit: Casper Star Tribune	Click to Enlarge   A fire near Lander caused by down power poles raged for hours while over 5,000 residents were without power.   Photo Credit: County 10

 TOP MENU

Learn more about the National Weather Service's efforts to build a Weather-Ready Nation!